Presently, in glass blowing machinery employed in the prior art, a gob of molten glass is suspended above a hollow actuable plunger piston. Applicant is aware of plunger pistons manufactured by Maul and by Emhart. The plunger piston is actuated so as to telescope along an inner hollow piston journalled within the longitudinal cavity within the hollow plunger piston. The plunger piston extends telescopically over the inner piston so as to drive a perforated plunger, located at the distal end of the plunger piston, into the gob of molten glass. A stream of air is forced along the longitudinal cavity within the inner piston and the longitudinal cavity within the plunger piston so as to exit the perforations in the plunger.
Occasionally a jam occurs causing glass from the gob of molten glass to fall downwardly through the perforations or holes in the plunger. Some of the glass falling through the perforations or holes in the plunger falls into the longitudinal cavities within the inner piston and plunger piston. This glass is blown out by the air stream and so does not cause a later problem. However, some of the glass falling through the perforations or holes in the plunger fall into the annular cavity formed between the inner piston and the plunger piston within the longitudinal cavity of the plunger piston. This glass, not being in the air stream, is not blown out and so may reside in the annular cavity until after the jam has been cleared and subsequent good ware is being formed. The glass residing in the annular cavity works itself out of the annular cavity, assisted by the subsequent telescoping actuation of the plunger piston relative to the inner piston, and is thus subsequently blown by the air stream into the good ware. This causes particles of glass to become lodged within the good ware, ruining the good ware. Glass residing within the annular cavity may also interfere with the function of the scraper bushing between the plunger piston and the inner piston so as to shorten the life of the scraper bushing.
It is the object of the present invention to provide a device to inhibit glass falling into the annular cavity.